Polypropylene composition for foaming

ABSTRACT

The present invention relates to a new polypropylene composition for molded articles, such as finished parts for the automotive industry. A composition comprising: (A) from 40 to 85% by weight of a first propylene-based component being selected from propylene homopolymers, propylene copolymers and heterophasic propylene polymer, such first propylene-based component having a flexural modulus higher than 800 MPa; (B) from 5 to 20% by weight of a second propylene-based component being a heterophasic propylene polymer comprising: (B1) from 20 to 90% by weight of a crystalline polypropylene, and (B2) from 10 to 80% by weight of a copolymer of ethylene and at least one C 3 -C 10  alpha-olefin, such copolymer containing from 10 to 70% by weight of ethylene, being soluble in xylene at room temperature, and having an intrinsic viscosity in tetrahydronaphtalene at 135° C. of higher than 3.5 dl/g; and (C) from 10 to 40% by weight of glass fibers.

FIELD OF THE INVENTION

The present invention relates to glass-fiber-reinforced thermoplasticpolypropylene compositions for use in foaming of molded articles havingsmooth surface and an inner foam structure.

BACKGROUND OF THE INVENTION

Typically, integrally foamed articles having smooth, mold-imprintedsurfaces are used in trim components for interior designs, e.g. in carsor airplanes. Due to their free-flowing characteristics, differentblends filled with talcum have been used in such applications hitherto.The potential of talcum-reinforced blends is limited for integralfoam-molding of rigid finished articles, such as car dashboards, due totheir inherent low flexural stiffness. Further, the relative volumetricincrease during foaming is limited. Nonetheless talcum blends, due totheir excellent free-flowing properties, have allowed achieving a veryuniform, homogenous foam structure and foam cell separation pattern,without inner delamination of the foam or widespread cell disrupturetaking place.

It would be desirable to avoid the disadvantages of the prior art and todevise a new composite material improving volumetric gain in integralfoaming of molded articles whilst retaining the advantages of the priorart blends used in foaming, notably their excellent free-flowingproperties and uniform cell forming characteristics.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is a compositioncomprising:

-   (A) from 40 to 85% by weight of a first propylene-based component    being selected from propylene homopolymers, propylene copolymers and    heterophasic propylene polymer, such first propylene-based component    having a flexural modulus determined in accordance with ISO 178    higher than 800 MPa;-   (B) from 5 to 20% by weight of a second propylene-based component    being a heterophasic propylene polymer comprising:-   (B1) from 20 to 90% by weight, preferably from 50 to 90%, of a    crystalline polypropylene, and-   (B2) from 10 to 80% by weight, preferably from 15 to 60% by weight,    of a copolymer of ethylene and at least one C3-C10 alpha-olefin,    such copolymer containing from 10 to 70% by weight, preferably from    10 to 50% by weight, of ethylene, being soluble in xylene at room    temperature, and having an intrinsic viscosity in    tetrahydronaphtalene at 135° C. of higher than 3.5 dl/g, preferably    higher than 4 dl/g, more preferably of from 5 to 8 dl/g; and-   (C) from 10 to 40% by weight of glass fibers.

The sum of the percentage amounts of the individual components of thecomposition equal to 100 percent.

DETAILED DESCRIPTION OF THE INVENTION

The first propylene-based component (A) can suitably be a propylenehomopolymer or copolymer containing up to 5% by weight of ethylene andoptionally one or more C₄-C₁₀ alpha-olefin(s). Examples of C₄-C₁₀alpha-olefins that may be used as comonomers include 1-butene,1-pentene, 1-hexene, 4-methyl-l-pentene and 1-octene, with 1-butenebeing particularly preferred.

As a suitable alternative, the component (A) can be a heterophasicpropylene polymer containing from 5to 25% by weight of a copolymer ofpropylene and ethylene, such copolymer containing from 40 to 60% byweight of ethylene. Suitably said component (A) has a MFR (230 ° C.,2.16 kg) value of from 10 to 150 g/10 min.

Also suitably, said component (A) has a content of xylene-solublefraction (at 25° C.) of less than 7% by weight, preferably of less than5% by weight, even more preferably of less than 2% by weight.

Generally said component (A) has amount of isotactic pentads higher than95%. The component (B) can suitably be prepared by a sequentialpolymerization, comprising at least two sequential steps, whereincomponents (B1) and (B2) are prepared in separate subsequent steps,operating in each step in the presence of the polymer formed and thecatalyst used in the preceding step.

Within the second propylene-based component (B) the component (B1) cansuitably be a crystalline propylene (co)polymer being for at least 85%by weight, preferably at least 90% by weight, more preferably at least95% by weight, insoluble in xylene at 25° C.

Within the second propylene-based component (B) the component (B2) cansuitably be an ethylene copolymer containing from 15 to 60% by weight,preferably from 20 to 40% by weight of a C3-C10 alpha olefin, preferablypropylene, being for at least 60% soluble in xylene at room temperature.Polymer compositions suitable as component (B) are those disclosed inInternational Application WO 02/28958, specifically compositionscomprising (percent by weight):

-   A) 20%-90% of a crystalline polypropylene component containing from    25% to 75% of a fraction A^(I) having a melt flow rate MFR^(I) of    from 0.5 to 10 g/10 min., and from 75% to 25% of a fraction A^(II)    having a melt flow rate MFR^(II) such that a ratio MFR^(II)/MFR^(I)    is from 30 to 2000, preferably from 50 to 1000; and wherein    fractions A^(I) and A^(II) are independently selected from the group    consisting of a propylene homopolymer, a random copolymer of    propylene containing up to 8% of ethylene, and a random copolymer of    propylene containing up to 8% of at least one C4-C10 alpha-olefin;    and-   B) 10%-80% of a copolymer component of ethylene and at least one    C3-C10 alpha-olefin, the copolymer containing from 10 to 70% of    ethylene, and optionally minor amounts of a diene, said copolymer    being soluble in xylene at room temperature, and having an intrinsic    viscosity in tetrahydronaphtalene at 135° C. of from 4 to 9,    preferably 5 to 8, most preferably 5.5 to 7 dl/g.

Other polymer compositions suitable as component (B) are those disclosedin International Application WO 2004/087805, specifically compositionscomprising (percent by weight):

-   A) 50-90% of a crystalline polypropylene component comprising:-   A^(I)) from 25 to 75% of a fraction having a melt flow rate MFR^(I)    of from 0.1 to 10 g/10 min.; and-   A^(II)) from 25 to 75% of a fraction having a melt flow rate value    MFR^(II) equal to or lower than 100 g/10 min.;    wherein the ratio MFR^(II)/MFR^(I) is from 5 to 60, and the    fractions (A^(I)) and (A^(II)) are independently selected from the    group consisting of a propylene homopolymer, a random copolymer of    propylene containing up to 3% of ethylene, and a random copolymer of    propylene containing up to 6% of at least one C4-C10 alpha-olefin;    and-   B) 10%-50% of a copolymer component of ethylene and at least one    C3-C10 alpha-olefin, the copolymer containing from 15% to 50% of    ethylene and optionally minor amounts of a diene; said composition    having a value of the intrinsic viscosity of the fraction soluble in    xylene at room temperature (about 25° C.) equal to or higher than    3.5 dl/g.

According to the present invention, it is neither necessary nor desiredto crosslink the components (A) and (B) by vulcanization.

The glass fibers (C) suitably have a length of from 0.1 to 20 mm,preferably from 0.3 to 1.0 mm, when measured in the final compound, andalso suitably have a diameter of less than 50 μm, preferably of from 10to 15 μm. The glass fibers are of short length, such as to allow ofsimple process engineering of the thermoplastic composition of theinvention. Long glass fibers, whilst known to convey enhanced stiffnesscharacteristics, require special processing methods as to preventshearing and breakage of such long fibers. Short glass fibers, however,require nucleation for attaining a similar stiffness of the ensuingmolding composition, in particular when using cut glass fibers.

Further preference is given to using cut glass fibers, also known aschopped strands. Such preferred glass fibers have a length of from 3 to8 mm, more preferably of from 3 to 6 mm, before compounding, and of from0.1 to 1.5 mm after compounding, and have a diameter of from 5 to 25 μm,preferably of from 10 to 15 μm. Glass fibers obtained from commercialsource are pretreated with a usually polar-functionalizedcompatibilizer, as the skilled person well knows. Such compatibilizerserves to make the glass fibers less hydrophilic and therefore morecompatible with the polymer, allowing the glass fiber to bind moreeffectively to the polyolefin matrix.

The compositions of the present invention have preferably a melt flowrate value (ISO 1133- 230° C., 2.16 Kg) of from 10 to 150 g/10 min,preferably of from 70 to 120 g/10 min.

Optionally, the composition of the present invention may comprise anucleator for physical foaming by gas injected and physically dissolvedinto the polymer. Said nucleator can suitably be talc, lithiumcarbonate, a zeolite or a mixture thereof

Further optionally the composition of the present invention may comprisetalc in amounts preferably not higher than 3% by weight.

The compositions of the present invention can be prepared bymechanically mixing its components.

The compositions of the present invention suitably show flexural modulushigher than 1500 MPa, preferably higher than 2000 MPa, more preferablyhigher than 3000 MPa.

The compositions of the present invention also suitably show tensilemodulus higher than 1500 MPa, preferably higher than 2000 MPa, morepreferably higher than 3000 MPa.

The compositions of the present invention further suitably show aC-emission value of less than 50 g/10 min, preferably of less than 20g/10 min.

The compositions of the present invention, due to the combination ofproperties (high stiffness, high flowability and good impact behavior)are particularly suitable for integral foaming of molded articles suchas finished parts for the automotive industry, e.g. instrument panels ofcars.

Accordingly, another object of the present invention is a foamed articleprepared from a composition according to the invention. Said foamedarticles, which are not obtained by reactive modification byvulcanization, have suitably a density of from 0.5 to 1.1 g/cm3. Theycan be integrally foamed article, wherein the average cell size ispreferably of from 5 to 500 μm.

A suitable process for integral foaming of molded articles is theso-called ‘breathing mold process’ illustrated in FIG. 1. The melt isinjected into the mold, as in conventional injection molding. Prior toinjection however, during melting and extrudating of the melt, an inertgas is added under pressure, to be physically dissolved and homogenizedin the melt (physical foaming). It is likewise possible to use chemicalblowing agents, either optionally or in conjunction with such gas.Typical chemical blowing agents are inert, volatile liquids, such ase.g. lower hydrocarbons, having a boiling point of higher than 80° C.whose expansion is triggered by heating the mold. Other examples arehydrogen carbonates which release carbon dioxide under heat. It is alsopossible to add such chemical blowing agents contained in microspheres,which microspheres allow of easier homogenization and handling and whichare disrupted upon expansion. Typically, such integral foams have asandwich structure, as essentially derived from expansion of a moldedsheet; both the parallel, large surfaces flanking, as in sandwich, thefoam layer, retain their dense structure as in the original sheet. Afterinjection in the mold of gas-loaded melt, the mold volume filled withthe melt polymer is caused to increase and the foam is thus formed.

Foamed articles according to the present invention can be, for example,finished parts for the automotive industry, such as dashboards,instrument panels or other interior trim components for a car.

According to a further object, the present invention provides a vehicle,such as a car or a truck, comprising a foamed article according to theinvention. The following examples are given to illustrate the presentinvention without any limiting purpose.

EXAMPLES Measurement Methods

The characterization data for the propylene polymers and for theobtained films were obtained according to the following methods:

Melt Flow Rate (MFR)

Determined according to ISO 1133 (230° C., 2.16 Kg).

Flexural Modulus

Determined according to ISO 178.

Tensile Modulus

Determined according to ISO 527/1+2.

Charpy

Determined according to ISO 179/1eU and/1 eA.

Xylene Solubles (XS)

Determined as follows: 2.5 g of polymer and 250 ml of xylene areintroduced in a glass flask equipped with a refrigerator and amagnetical stirrer. The temperature is raised in 30 minutes up to theboiling point of the solvent. The so obtained clear solution is thenkept under reflux and stirring for further 30 minutes. The closed flaskis then kept in thermostatic water bath at 25° C. for 30 minutes. The soformed solid is filtered on quick filtering paper. 100 ml of thefiltered liquid is poured in a previously weighed aluminium container,which is heated on a heating plate under nitrogen flow, to remove thesolvent by evaporation. The container is then kept on an oven at 80° C.under vacuum until constant weight is obtained. The weight percentage ofpolymer soluble in xylene at room temperature is then calculated.

Determination of Isotactic Pentads Content

Determined as follows: 50 mg of each xylene insoluble fraction weredissolved in 0.5 mL of C2D2C14. The 13C NMR spectra were acquired on aBruker DPX-400 (100.61 Mhz, 90° pulse, 12 s delay between pulses). About3000 transients were stored for each spectrum; mmmm pentad peak (21.8ppm) was used as reference. The microstructure analysis was carried outas described in literature (Polymer, 1984, 25, 1640, by Inoue Y. et Al.and Polymer, 1994, 35, 339, by Chujo R. et Al.).

All compositions described in the examples were produced with atwin-screw extruder Krupp Werner & Pfleiderer/1973, ZSK 53, screwdiameter: 2×53, 36D with a screw rotation speed of 150 rpm and a melttemperature of 230° C. to achieve the compounds for foaming tests.

All compounds were foamed under the same processing conditions with aBattenfeld BA 1500/630 injection molding machine, melt temperature: 220°C., mold temperature: 35 ° C., injection pressure: 1500 bar, either withphysical blowing agent (0.3% nitrogen) or with chemical blowing agent(2% Hydrocerol ITP 815). The high pressure foam process was used toproduce the foamed flat plates. After injection under high pressure thematerial starts foaming when opening the mold by a controlled distance.This opening distance controls the final thickness of the part and thusthe final density.

Example 1 (Comparative)—Composition

The composition was built up with:

-   -   75.1% Moplen EP600V, a heterophasic copolymer available from        LyondellBasell having MFR (ISO 1133-230° C., 2.16 Kg) of 100        g/10 min;    -   1% Moplen HP500N, a homopolymer available from LyondellBasell        having MFR (ISO 1133-230° C., 2.16 Kg) of 12 g/10 min;    -   0.2% Irgafos 168 (tris(2,4-di-tert-butylphenyl)phosphite);    -   0.3 Irganox 1010        (pentaerythriltetrakis(3-(3,5-die-tert-butyl-4-hydroxyphenyl)propionate));    -   0.1% zinc oxide;    -   1% BK MB-PE 4687 (Cabot) black masterbatch;    -   20% short glass fiber ECS 03T-496 chopped strands (NEG), having        a length of 4 mm and a diameter of 13 μm;    -   1% coupling agent, MAH grafted polypropylene;    -   0.1% Hostanox SE 10 (dioctadecyldisulphide);    -   0.2% Crodamide ER (Erucamide, (Z)-Docos-13-enamide);    -   1% Talc Luzenac 1445 (hydrated magnesium silicate).

The properties of the final unfoamed composition are reported in table1.

Example 2—Composition

The composition was built up with:

-   -   65% Moplen EP600V, a heterophasic copolymer available from        LyondellBasell having MFR (ISO 1133-230° C., 2.16 Kg) of 100        g/10 min;    -   10.1% Hifax X 1956 A, a reactor-made TPO (thermoplastic        polyolefin) available from LyondellBasell having MFR (ISO        1133-230° C., 2.16 Kg) of 1.2 g/10 min, an intrinsic viscosity        in tetrahydronaphtalene at 135° C. of the fraction soluble in        xylene at room temperature of 7 dl/g, being built up with 35%        homopolymer with MFR (ISO 1133-230° C., 2.16 Kg) of 73 g/10 min,        35% homopolymer with MFR (ISO 1133-230° C., 2.16 Kg) of 1,2 g/10        min, and 30% ethylene/propylene copolymer with 36% by weight of        ethylene units;    -   1% Moplen HP500N, a homopolymer available from LyondellBasell        having MFR (ISO 1133-230° C., 2.16 Kg) of 12 g/10 min;    -   0.2% Irgafos 168 (Tris(2,4-di-tert-butylphenyl)phosphit);    -   0.3% Irganox 1010 (Pentaerythrittetrakis (3 -(3,5        -die-tert-butyl-4-hydroxyphenyl)propionat));    -   0.1% zinc oxide;    -   1% BK MB-PE 4687 (Cabot) black masterbatch;    -   20% short glass fiber ECS 03T-496 chopped strands (NEG), having        a length of 4 mm and a diameter of 13 μ;    -   1% coupling agent, MAH grafted polypropylene;    -   0.1% Hostanox SE 10 (Dioctadecyldisulfid);    -   0.2% Crodamide ER (Erucamide, (Z)-Docos-13-enamid);    -   1% Talc Luzenac 1445 (hydrated magnesium silicate).

The properties of the final unfoamed compositions are reported in table1.

TABLE 1 Ex. 1-comparative Example 2 MFR [g/10 min] 45 20 Tensile modulus[MPa] 4700 4500 Flexural modulus [MPa] 4000 4200 Charpy notched at RT[KJ/m2] 7 11

Examples 3 (Comparative), 4 and 5—Foamed Articles

The compositions of examples 1 (comparative) and 2 were submitted tofoaming by mold opening (“breathing mold”) to obtain flat plates with1.6 mm thickness and 1.07 g/cm3 density. The samples were foamed eitherwith a chemical agent (2% Hydrocerol ITP 815) or with a physical agent(nitrogen). Table 2 shows the results. The foaming behavior is describedas a function of the opening distance. As it can be seen, thecomposition used in comparative example 3 shows a good foaming behaviorby opening the mold from 1.6 mm to 2.8 mm. At a higher opening distanceno foaming process was possible because the foam became destroyed bycell wall rupture. The outer layers of the foamed plate delaminated dueto the destroyed foam structure. The lowest achievable density was 0.61dl/g. Conversely, the compositions used in example 4 survived theprocess also by opening the mold up to 3.6 mm, which means that it ispossible to realize higher density reduction with this material. A finaldensity of 0.47 dl/g could be achieved. Example 5 shows that it is alsopossible to use this material for foaming with physical blowing agents.By opening the mold from 1.6 mm to 4.6 mm a final density as low as 0.37dl/g could be achieved.

TABLE 2 Example 3-comparative Example 4 Example 5 Material Example1-comparative Example 2 Example 2 Blowing agent chemical chemicalphysical Plate thickness 2.1 2.8 3.7 2.1 3.0 3.6 3.0 3.7 4.6 afterfoaming [mm] Total density [dl/g] 0.81 0.61 0.46 0.81 0.57 0.47 0.570.46 0.37 Cell structure closed closed open closed closed closed closedclosed closed Average cell size 0.14 0.17 n. a. 0.15 0.20 0.20 0.26 0.220.2 [mm] (method: nominal diameter) Delamination no No yes no no no nono no Foaming behavior good good bad good good good good good good

A composition comprising:
 1. (A) 40-85% by weight of a firstpropylene-based component being selected from propylene homopolymers,propylene copolymers and heterophasic propylene polymer, such firstpropylene-based component having a flexural modulus determined inaccordance with ISO 178 higher than 800 MPa; (B) 5-20% by weight of asecond propylene-based component being a heterophasic propylene polymercomprising: (B1) 20-90% by weight of a crystalline polypropylene, and(B2) 10-80% by weight of a copolymer of ethylene and at least one C3-C10alpha-olefin, such copolymer containing from 10-70% by weight ofethylene, being soluble in xylene at room temperature, and having anintrinsic viscosity in tetrahydronaphtalene at 135° C. of higher than3.5 dl/g; and (C) 10-40% by weight of glass fibers.
 2. The compositionof claim 1, wherein the copolymer (B2) has an intrinsic viscosity intetrahydronaphthalene at 135° C. of from 5-8 dl/g.
 3. The compositionaccording to claim 1, wherein the component (B) comprises (percent byweight): A) 20%-90% of a crystalline polypropylene component containing25-75% of a fraction A^(I) having a melt flow rate MFR^(I) of 0.5-10g/10 min., and 25-75% of a fraction A^(II) having a melt flow rateMFR^(II) such that the ratio of MFR^(II)/MFR^(I) is 30-2000; and whereinfractions A^(I) and A^(II) are independently selected from the groupconsisting of a propylene homopolymer, a random copolymer of propylenecontaining up to 8% of ethylene, and a random copolymer of propylenecontaining up to 8% of at least one C₄-C₁₀ alpha-olefin; and B) 10%-80%of a copolymer component of ethylene and at least one C₃-C₁₀alpha-olefin, the copolymer containing 10-70% of ethylene, andoptionally minor amounts of a diene, said copolymer being soluble inxylene at room temperature, and having an intrinsic viscosity intetrahydronaphtalene at 135° C. of 4-9.
 4. The composition according toclaim 1, wherein the component (B) comprises (percent by weight): A)50-90% of a crystalline polypropylene component comprising: A^(I))25-75% of a fraction having a melt flow rate MFR^(I) of 0.1-10 g/10min.; and A^(II)) 25-75% of a fraction having a melt flow rate valueMFR^(II) equal to or lower than 100 g/10 min.; wherein the ratioMFR^(II)/MFR^(I) is from 5-60, and the fractions (A^(I)) and (A^(II))are independently selected from the group consisting of a propylenehomopolymer, a random copolymer of propylene containing up to 3% ofethylene, and a random copolymer of propylene containing up to 6% of atleast one C₄-C₁₀ alpha-olefin; and B) 10%-50% of a copolymer componentof ethylene and at least one C₃-C₁₀ alpha-olefin, the copolymercontaining from 15-50% of ethylene and optionally minor amounts of adiene; said composition having a value of the intrinsic viscosity of thefraction soluble in xylene at room temperature (about 25° C.) equal toor higher than 3.5 dl/g.
 5. The composition according to claim 1,wherein the glass fibers (C) have a length of from 0.1-20 mm, and have adiameter of less than 50 μm.
 6. The composition according to claim 1,having a melt flow rate value (ISO 1133-230° C., 2.16 kg) of from 10-150g/10 min preferably of from 70 to 120 g/10 min.
 7. A foamed articleprepared from the composition of claim
 1. 8. A foamed article of claim7, comprising a finished part for use in the automotive industry.
 9. Avehicle comprising the foamed article of claim 8.